The present invention relates to heat transfer element baskets and, more specifically, to an assembly of heat absorbent plates in a basket for use in a heat exchanger wherein heat is transferred by means of the plates from a hot heat exchange fluid to a cold heat exchange fluid. The present invention has particular application in heat transfer apparatus of the rotary regenerative type wherein the heat transfer element plates carried in such baskets are heated by contact with a hot gaseous heat exchange fluid and thereafter brought in contact with a cool gaseous heat exchange fluid to which the heat transfer element gives up its heat. The element basket of the present invention is most advantageously suited for use in the hot end of a rotary regenerative heat exchanger.
One type of heat exchange apparatus commonly used for gas-to-gas heat exchange in the process industry and for gas-to-air heat exchange on utility steam generators is the well-known rotary regenerative heat exchanger. Typically, a rotary regenerative heat exchanger has a cylindrical rotor divided into sector-shaped compartments in which are disposed a mass of heat transfer element which, as the rotor turns, is alternately exposed to a stream of heating gas and then upon rotation of the rotor to a stream of cooler air or other gaseous fluid to be heated. The heat absorbent mass typically comprises a plurality of heat transfer element basket assemblies mounted in sector shaped compartments. Each of the heat transfer element basket assemblies houses a plurality of heat transfer plates which when exposed to the heating gas absorb heat therefrom and then when exposed to the cool air or other gaseous fluid to be heated, the heat absorbed from the heating gas by the heat transfer plates is transferred to the cooler gas.
Most commonly, such an element basket comprises a frame-like housing having a plurality of sheet-like heat transfer plates disposed therein. Typically, the element basket housing comprises a frame formed of a pair of spaced plate-like end members held together by paired side straps interconnecting the end members along the sides thereof such as shown in U.S. Pat. Nos. 3,314,472; 4,561,492 and 4,606,400. A plurality of heat transfer plates are stacked in closely spaced relationship within the basket housing to provide a plurality of passageways between adjacent plates through which the heat exchange fluids pass. The side straps which interconnect the spaced end members typically extend in pairs along the opposite sides of the stacked array of heat exchange elements. On each side of the heat exchange element is a first side strap extending between the upper regions of the spaced end members and a second side strap extending between the lower region of the end members in spaced, parallel relationship to the first side strap. The side straps may be flanged inwardly along the longitudinal edge lying at the edge of the basket assembly to provide a retaining surface for preventing the heat transfer plates from falling out of the open ends of the element basket as shown in U.S. Pat. No. 3,314,472.
Element baskets have also been constructed in the past with a box-like housing as shown in U.S. Pat. No. 3,379,240. As depicted therein, the element basket is formed of a solid sheet folded into a generally U-shaped member having a base end and two outwardly extending, diverging legs. A solid accurate end plate is welded between the outward end portions of the legs of the U-shaped member after the heat exchange element sheets have been stacked within the housing defined by the U-shaped member. A resilient curved pressure member is disposed between the stacked element sheets and the base end of the U-shaped member to ensure that a compressive force is imposed against the stacked element to keep the element sheets in a tightly packed array against the end plate welded between the legs of the U-shaped member.
Whether the element basket is in the form of a frame-like housing or a box like housing, a plurality of retaining bars are typically welded between the end members across the top and bottom ends thereof to further assist in keeping the heat transfer element plates from falling out of the open ends of the element basket. The retaining bars may merely be disposed to lie across the top and bottom edges of the heat transfer element plates as shown in U.S. Pat. No. 4,561,492. Alternatively, in order to provide a shorter basket for a given plate height, the retaining bars may be disposed within recesses cut in the top and bottom edges of the heat transfer element plates as shown in U.S. Pat. No. 4,606,400.
The retaining bars also serve as structural members for supporting lifting means to facilitate handling of the assembled element baskets and, in particular, to facilitate the installation and removal of the element baskets from the heat exchanger. Typically, the lifting means comprises a pair of spaced apart holes formed in a centrally located retaining bar as shown in U.S. Pat. No. 4,552,204, or a pair of spaced apart pins integral with and passing through a centrally located retaining bar as shown as in U.S. Pat. No. 4,557,318. When the lifting means comprises a pair of holes in the aforementioned U.S. Pat. No. 4,552,204, the element basket is lifted by means of a pair of clevis means which are disposed to span the central retaining bar about each lifting hole. Each clevis is engaged to the retaining bar by a pin which is passed through the lifting hole and each side of the clevis spanning the bar. When the lifting means comprises a pair of lifting pins as in the aforementioned U.S. Pat. No. 4,557,318, the element basket is lifted by means of a pair of lifting lugs which simply grasp the pins extending through the central retaining bar.
Such prior art element baskets have performed well over the years. However, such box-like element baskets are limited in use because of their weight to the cold end of the heat exchanger as baskets in the cold end are generally only about a foot deep. Due to the solid wall structure of such box-like element baskets, the weight and the material costs of deeper box-like baskets would be excessive. Prior art frame-like baskets, while being lighter than similarly sized box-like baskets, are more labor intensive to produce due to the number of separate members which must be welded together to form the frame-like housing. Additionally, distortion of the bar-like members may occur during the welding together of the frame which can lead to difficulty in maintaining proper tolerances.
It is an object of the present invention to provide an improved element basket assembly wherein the element basket is of a frame-like construction but which is less suspectable to distortion and less labor intensive to assemble than prior art frame-like baskets, while also being lighter than prior art box-like baskets of similar size.